Basic Guides: Electric Substation

Design

Colegio de Ingenieros y Agrimensores de Puerto RicoDoeg Rodríguez and Angel T. Rodríguez Barroso

March 31, 2010San Juan, P.R.

Objective

The seminar’s objective is to provide a basic knowledge of the process of designing an electrical substation.

Electrical Substation

An assembly of equipment in an electric system through which electrical energy is passed for generation, transmission, distribution, interconnection, transformation, conversion or switching.

Basic ConceptsElectrical Substation Design

Substation Types:Functions

Generator step-upTransmission Center

Distribution

Generator Step-Up

Transmission Center

.

230/115/38 KV Transmission Center

230/115 KV Transmission Center

Distribution Substation

Industrial Substation

Industrial Substation

Basic ConceptsSubstation Types

Substation Types:

Insulating Medium

Air Insulated Gas Insulated

Air Insulated (AIS)

GIS Substation

GIS Substation

GIS Substation

GIS Substation

GIS Substation

Substation ProjectBasic Concepts

Process starts with a need System deficiency is identified

System Deficiencies.docSystem Studies.docDevise a project plan

Project scope is documentedAn estimate is developed and approved

Formal plans and drawings are developedRecordsDrawingsMaterial list and specifications

ScopeDescription including references to other elements

Single-line diagramsEstimates including soft and hard costs

System restrictionsTime constraints

Operational restrictionsTeam

Diseño Sub-w\Copy of Industrial Complex B Scope.doc

General Design ProcedureSystem deficiencies are definedProject scopePreliminary designPreliminary design approvalFinal DesignFinal Design approvalEstablish Project Time Table

Basic DocumentsSite information as permits, surveys,

geological surveys, equipment specifications, restrictions, and legal contracts

Construction drawingsSupplier list

Basic/Elements/ DrawingsCover sheetDrawing listSingle line diagram (S) Protection Single lineThree line diagramSite grading/civil Grounding and FenceFoundationEquipment layoutLine feed cables

Structure detailsConduits, racks & racewaysCable plansControl buildingStation service AC-DC Cable listSchematics AC-DCControl panel wiringEquipment/breakers-

transformers/ wiringCommunication Facilities integration

DrawingsSingle Line Diagram

Is the station reference Presents orientation & interconnections of equipmentPresents switching & functional relay information

Three Line DiagramThree phase line diagramDefine PhasingCircuit breaker pole numbersDisconnect switchesCT / VT connections & ratioCablesTransformer information & connectionsArresters

DrawingsAC Schematics

Is a document to establish current CT and voltage VT circuits interconnections with relays and metering

DC SchematicsIs a document to establish relay, control and circuit interruption interconnections

RUS Bulletin1724ERUS 1724E Drawing Checklist

appendix A page 73SUB-SJ006.pdf

Cover SheetDrawing List

Survey &

Site

SiteSite

Diseño Sub-w\VIEQ Electrical Site .pdf

Single Line

Diagram

Single Line DiagramSingle Line Diagram

Diseño Sub-w\Single line-1a.pdf

Equipment

Layout

Equipment LayoutGeneral System Layout

Diseño Sub-w\VIEQ Subst Profile 1.pdfAerial Photograph V.pdf

Grounding

& Fence

Grounding StudySeminario Grounding CEM-1.ppt

Combine-grounding.pdf

GroundingDiseño Sub-w\VIEQ Grounding 1.pdfDiseño Sub-w\SVC Grounding 2.pdf

Three Line

Diagram

Three Line Diagram Example

Diseño Sub-w\LMM AC CT VT.pdf

Line

Feed

Line Feed ExampleDiseño Sub-w\SVC Primary Dist.pdf

Cable StudyAmpacity Cable Studies

Report-Cable-Sub-DIS.pdf

Panel & Control

Wiring

DCDiagrams

Preliminary DesignPreliminary Information Required

Is a new site or existing ?If existing, get the last drawings

What are the design standardsDescription of existing propertyPlanning studyIndustry expansion plan

First Visit to the SiteObserve all site advantages and constraints

Site restrictions (urban regulations)Check for future expansion constraintsHow lines and load circuits will be brought to the site and exit outAccess to the site (how to move heavy equipment)

First Visit to the SitePower Line Supply

Line Voltage Consider how to maintain the substation in service without one, or two lines out of serviceOverhead or underground

Restrictions for line construction, regulations

Emergency Generator integration

Load CircuitsLine voltageConsider how to enter a building or exit the stationOverhead or underground

See future expansionplans & design accordingly

First Visit to the SiteIs the site has a good construction and maintenance access?

If existing substation, does it allows for outages?Does it provides for public and workers safety?

Observe drainage patternsFlat terrain or hillside

Run off patternsWhat are the aesthetics requirements?

Check for potential zoning, environmental or other problemsVerify local or government special regulations

Post First Visit to SiteUpdate project scope & get approval if

requiredUpdate estimate if required

Submit amended permits if requiredAdjust any design criteria if required

Issue instructions for long lead equipment and site studies

Equipment Lead Time

Substation Transformers 10 -16 monthsCircuit Breakers 4 – 8 monthsHigh Voltage Switches 4 – 8 monthsControl & Protection Panel 4 – 8 monthsHigh Voltage GIS Equipment 8 – 12 months Medium Voltage GIS 8 – 10 months

Developed Project Time TableExpected Service DatePermitsEquipment Procurement (transformers, breakers, etc. lead time)Power supplier requirements (PREPA and others)Client operations inputGet the approval:

SLD drawing Site Layout Detailed design ConstructionCommissioning and as-built

RUS Bulletin 1724ESubstation Design Summary

SUB-SJ007.pdf

Bus ArrangementsReliability

Cost of configurationAvailable space

Basic configurationsSingle busSingle bus with tie breakerMain & transfer busRing busBreaker & a halfDouble bus

Optimum Bus configurationOutage costsType of bus or customerMaintenance costSystem securityLoad characteristicsFailures effect in the systemLocation of the bus

Bus Arrangements

Cost of configuration Cost SpaceSingle bus $1.00 P.U. 1.0Single bus with tie breaker $1.22 P.U. 1.2Main & transfer bus $1.38 P.U. 1.7Ring bus $1.15 P.U. 1.2Breaker & a half $1.63 P.U. 2.0Double bus Double breaker $2.06 P.U. 3.0

SUB-SJ005.pdf

Surge ArrestersFunctions:

Limit transient surge voltages below the insulation breakdown of the equipment

Provide transient voltage protection while connected to the power operating voltage

Surge Arrester SelectionAll arresters use Zinc Oxide valves (MOV)For selecting you will need:

Power operating voltage ratingEnergy dissipation capabilityType or arrester classInsulation coordination study

TransformersSome of the Standards applied

IEEE STD C57.12.2000 ANSI STD C57.12.10-1997 IEEE STD C57.12.90-1999IEEE STD C57.12.01-2000IEEE STD C57.98-1993IEEE STD C57.91-1995IEEE PC 57.119 (Draft 14.0) 2001

TransformersRating

Self cooled ONAN oil natural, air natural circulation

Forced Air Rating ONAF oil natural, air forced circulation

Forced Oil Rating OFAF oil forced, air forced circulation

RatingTransformers 2.5-10 MVA

One 125% stage coolingTransformers >10 MVA

Two cooling stages 133% ONAN166% ONAN

Continuous loading with oil hot spot less than 110 degree C

Short term loading 180 degree C

TransformersOil Preservation

Sealed tankInert Gas

Nitrogen blanket over oilModified Conservator

Main tank is filled of oil from a conservator tank

Winding connectionsDelta-Wye

NLT, LTC location?Wye –Delta

NLT, LTC location?Delta –Delta

NLT, LTC location?Three winding transformers

NLT, LTC-location

BreakersDefinition:

Is an automatically operated electromechanical device designed to protect an electrical circuit from damage caused by a short circuit or an overload

Breakers Type

There are different classifications

Interrupting mediumAir blastingOil (high & low volume)Vacuum (medium voltage)Gas SF6 (high voltage)Magnetic Air (distribution)

TankDead tankLive tank

Ratings – ANSI C37.06Rated voltageInsulation levelContinuous currentInterrupting current at rated voltageTransient recovery voltageRated interrupting timePermissible trip delay

Disconnecting SwitchesTypes

StationTransmissionDistributionLow voltage

Switches

Station Power, Batteries ChargersAC Power

Two sources, emergency generator with transfer switch

Transformer cooling systemTransformer load tap changer Transformer cabinet heatersCircuit breakers stored energy

mechanismCircuit breakers cabinet heatersBuilding & Outdoor yard lightsBattery chargers & outletsBuilding mechanical systemBuilding A/C

DC ServiceTwo battery banks

Two DC distribution panelOne circuit per breaker from

each panel ( combine)For relay panel, one circuit

from each panelTwo circuit per transformer

Use IEEE Std 485 for sizing lead acid batteries

CablesHigh voltage cables

Follow PREPA regulations and buy cables from approved manufacturers

Shielded cable TR-Cross-linked PolyethyleneEthylene Propylene Rubber EPR

Low voltage Cables (600V)

Copper cable is more reliableMulticonductor, color code cable

is preferred Practice is:PT circuits #12 AWG CUCT circuits #10 or # 8 AWG CUControl Circuits # 14 AWG CUSCADA alarms #18 AWG CU

Protection

Relays are devices that are connected throughout the electric power system to detect an undesirable conditions and start an action to minimize damages to the system

Protection

Protection philosophy requires a balance between redundancy and cost

The goal is to protect the system with the simplest design

The more complex the protection scheme the more probability for bad operations

Substation LayoutSubstation LayoutSingle Line Diagram

Check:Numbers of breakers, disconnect switches, transformers,

auxiliaries, protective devices, lines and other equipment.Short circuit and current capacity of equipment, bus and other

equipmentCompliance with project’s scope and requirements Number of feeders and load circuitsThat all equipment fit within substation lot and complies with

standards

Substation LayoutFinalize design requirements

OutdoorHigh, low profile or GIS?

IndoorGIS or metal clad?

System protection and power company requirementsOverhead feeders and load circuits?

If overhead check clearancesUnderground feeder and load circuits?

Cables or Gas Insulated Lines or Bus (GIL, GIB)

Substation LayoutOutdoor Substation

Check:Compliance with all technical requirementsAll energize elements comply with the required clearances

ClearancesVerify compliance with the last requirements of the National

Electrical Safety Code or PREPA Diseño Sub-w\Copy of SVC Subst Profile 2.pdfDiseño Sub-w\Copy of SVC Subst Profile 3.pdf

If using outdoor metal clad substation: is protected from vehicle traffic? If using underground lines: are the manholes accessible?

Substation LayoutIndoor Substation

Check:Compliance with all technical requirementsIs the metal clad follow the NFPA Arc Flash guides? For maintenance clearances

GIS substation are considered safe and complies with all recommended guides

GIS-PDF\General-Layout-GIS.pdf

Substation DesignReferences

ANSI C37 series – Protection and Control EquipmentANSI C57 Series – Transformers

IEEE Standard 80- Substation GroundingNEMA Standards – Electric Equipment Construction

National Electrical Safety Code Rural Utilities Service Bulletin 1724E-300

(www.usda.gov/rus/electric/bulletin.htm)PREPA - Manual para el Diseño y Construcción de Mallas

Conectadas a Tierra de Subestaciones y EquiposPREPA -Reglamento Complementario al Código Eléctrico

Nacional

Questions?

Thank You

Substation Design An IntroductionDoeg Rodríguez

ATRB, Ingenieros CSP787-236-6900

Angel T. Rodríguez BarrosoMEC Engineering

605 Condado AvenueSan Juan, P.R.787-977-5045

angel.rodriguez@mecengpr.com